1. Field of Invention
The present invention relates to a submount, and more particularly to a submount having an island structure used for carrying a light-emitting element.
2. Related Art
The light-emitting principle of light-emitting diodes (LEDs) is to form a p-n junction with different doping modes. When electrons and holes are combined, the energy is released in the form of light, and the light is substantially a set of infinite multi-point light sources. LEDs are advantageous in high durability, long service life, light weight, and low power consumption. Besides, LEDs do not contain hazardous substances like mercury. Therefore, the illumination market has a high expectation on LEDs.
The light-emitting efficiency of LEDs is generally referred to as the external quantum efficiency (EQE) of an element, which is a product of the internal quantum efficiency (IQE) and light extraction efficiency (LEE) of the element. The IQE of an element is actually the electric-optical conversion efficiency of the element, which is mainly relevant to the characteristics of the element, such as the energy band, defects and impurities of the material of the element, as well as the expitaxy composition and structure of the element. The LEE of an element is the number of the photons generated inside the element that can be actually measured outside the element after being absorbed, refracted, and reflected by the element. Thus, factors related to the LEE includes the absorption coefficient and refractive index of the material of the element, the geometrical structure and surface roughness of the element, the refractive index difference between the element and the packaging material, and the type of the element packages, and so on. The product of the above two efficiencies is the light-emitting effect of the entire element, i.e., the EQE of the element.
Besides the prior art of face-up architecture, the face-down flip-chip type packages are the main trend of the future development, since the face-down flip-chip type packages can significantly improve the heat dissipation and light extraction effect. Currently, the flip-chip architecture may be classified into to two popular types including the thin film LED and the flip-chip LED. The thin film LED is mainly formed by turning over an expitaxy layer plated with a reflective layer to be fixed to a submount by a connection layer, and then stripping the growth substrate and roughening its upper surface. The flip-chip LED has a similar architecture as the above thin film LED. The main difference therebetween is that the flip-chip LED is fixed onto a submount through a plurality of metal balls, and thus a space for emerging light is formed between the expitaxy layer and the submount, so as to reduce the amount of absorption of the light emerging from below the flip-chip LED when being reflected back to the flip-chip LED.
FIG. 1 is a schematic view of a prior art flip-chip architecture. Referring to FIG. 1 the prior art of flip-chip architecture uses a metal ball 12 to fix a light-emitting element 11 onto a submount 13. However, the light emerging from below the light-emitting element 11 may still enter the light-emitting element 11 after being reflected by the surface of the submount 13, thus resulting in re-absorption and weakening the energy of the output light at last.